//
/******************************************************
        File name:    main.c
        Author:       Bitat (陆叁柒)
        Gitee :       https://gitee.com/bitat
        Email :       737166381@qq.com
        History:      2023/1/6
*******************************************************/


#include <stdio.h>

int main()
{
    int score  = 0;
    scanf("%d",&score);
    if(score>=90 && score<=100)
        printf("A\n");
    else if (score>=80 && score<=89)
        printf("B\n");
    else if (score>=70 && score<=79)
        printf("C\n");
    else if (score>=60 && score<=69)
        printf("D\n");
    else if (score>=0 && score<=59)
        printf("E\n");
    else
        printf("F\n");
    
    return 0;
}

